1. Field of the Invention
The present invention relates to a control system for catalytic processes. The present invention further relates to a control system for in processes for reforming hydrocarbon streams and for pollution remediation of exhaust streams.
2. Description of the Prior Art
Catalyst systems are employed extensively to reform light hydrocarbon streams, i.e. reduce methane and other light hydrocarbons to hydrogen, and to remediate exhaust streams, i.e. reduce/oxidize internal combustion exhaust to innocuous compounds.
A problem encountered with catalyst systems is poisoning of the catalyst. One source of such poisoning is adsorption/infiltration of oxygen-containing species such as carbon monoxide. Carbon monoxide interferes with the catalysis mechanism. Another source of poisoning is the deposition of carbon.
Methods of addressing catalyst poisoning include applying to the catalyst a direct current (DC) electric field and/or heating it to an elevated temperature, i.e. about 300° C. to about 800° C. Most commonly, an electric field and heat are concurrently applied. Application of a DC electric field and heat expels or pumps oxygen-containing molecular species from the catalyst. Application of DC current and/or heat to catalysts is described in the following: U.S. patent/application Ser. Nos. 2001/0000889 A1; 2002/0045076 A1; 4,318,708; 5,006,425; 5,232,882; 6,214,195; and 6,267,864. Such application is also described in the following literature references: Effect of Oxygen-containing Species on the Impedance of the Pt/YSZ Interface, Solid State Ionics, 100, 17 to 22 (1997); Transient and Permanent Effects of Direct Current on Oxygen Transfer across YSZ-Electrode Interfaces, Journal of the Electrochemical Society, 2479 to 2485, vol. 144, No. 7 (1997); and Thermodynamic Stability and Interfacial Impedance of Solid-Electrolyte Cells with Noble-Metal Electrodes, Journal of Electroceramics, 3:3, 279 to 299 (1999). The above U.S. patents/applications and literature references are incorporated herein in their entirety.
A problem encountered with application of a DC electric field to catalyst systems is a lack of a means for monitoring and sensing the level of poisoning present in the catalyst in real time or on a continuous basis. This lack of means to monitor and sense the level of poisoning in the catalyst in real time hinders precise and timely application of DC electric fields. Precise and timely application of DC electric field is important because if the field is too weak, the rate of expulsion of oxygen-containing species may be too low and such species may accumulate. If the DC field is too strong, the incidence of catalytically effective sites in the catalyst may be reduced.
The application of heat to catalyst systems also has the problem lack of real time control means but also suffers from imprecise effects of temperature on catalyst behavior and physical structure. If the temperature of the catalyst is too low, the catalyst may become fouled (dirty) and the kinetics of the catalyzed reaction may be negatively altered. If the temperature is too high, the kinetics of the catalyzed reaction may be negatively altered and/or the microstructure of the catalyst destroyed.
Other methods of addressing catalyst poisoning include chemical treatment and replacement of the catalyst. The chemical treatment is disadvantageous because continuous treatment is not possible and catalyst behavior is difficult to predict or control. Replacement of catalyst is expensive and requires shutdown of the process.
It would be desirable to have a system for controlling the application of a DC electric field and/or heat in a catalyst system. It would further be desirable to have a system for controlling the application of a DC electric field and/or heat in a catalyst system in a process for reforming hydrocarbon streams and for pollution remediation of combustion exhaust streams.